1. Field of the Invention
The present invention relates to an apparatus and method for differentially distributing a transmission power by a Base Station (BS) (a transmitter) to Mobile Stations (MSs) (receivers) depending on a channel state of each MS in a Space Division Multiple Access (SDMA) system.
2. Description of the Related Art
A Space Division Multiple Access (SDMA) system is a wireless communication system for allocating a radio resource to a plurality of Mobile Stations (MSs), at the same frequency at the same time, using a plurality of adaptive antennas. The SDMA system allocates the radio resource simultaneously to the plurality of MSs, thereby greatly increasing a system capacity. In the SDMA system, however, a Base Station (BS) allocates the radio resource to the plurality of MSs, at the same frequency at the same time, under circumstances where there is a fixed transmission power. Therefore, the transmission power for each MS should be divided.
The conventional SDMA system equally allocates the transmission power of the BS considering only the number of the MSs allocated the radio resource, at the same frequency at the same time, irrespective of a channel state of the MS. For example, if the MS allocated the radio resource, at the same frequency at the same time is three; the BS divides the transmission power by ⅓, and uses the divided transmission powers to transmit a signal to each MS. However, the MSs have different channel states from each other depending on location and time, respectively. Thus, fixed distribution of the transmission power irrespective of the channel state of the MS results in an excessive power for one MS and an insufficient power for another MS depending on the channel state of the MS. It thereby reduces a performance such as a data reception rate of an entire system.
Accordingly, an apparatus and method for differentially distributing a transmission power considering a channel state of each of a plurality of MSs when an SDMA system allocates a radio resource to the plurality of MSs, thereby enhancing a system performance is being required.